The present invention relates to ejector mechanisms for providing resiliently biased engagement between a first part of an electrical connector and a mutually engaging second part of the electrical connector mounted respectively on a circuit board and a back plane.
Electronic systems such as computers and telecommunications exchanges are typically constructed in a modular fashion from printed circuit boards (PCB), each circuit board generally performing a specific function. Each PCB requires multiple electrical connections which are generally provided by two part multi-pin electrical connectors which comprise a first part of the connector physically attached to the PCB and a second part attached to a rack, on a system chassis assembly, or a back plane circuit board, which acts as a socket for receiving the first part of the connector. Successful mating of the two parts is required in order to provide reliable electrical connection between the first and the second parts of the connectors.
Ejector mechanisms are user activated devices which are provided to load the PCBs into the system chassis or back plane circuit board to the effect of providing a biasing force which mutually couples the first and second parts of the electrical connectors. Correspondingly, the ejector mechanisms also facilitate ejection of the PCB from the system chassis so that the PCB may be replaced for example.
Known PCB ejector mechanisms typically comprise a lever arm formed on the PCB which is arranged in operation to engage a projection formed on the system chassis. Guide formations also formed on the system chassis or back plane assembly are arranged to receive the PCB and to guide the PCB into a load position in which the first and second parts of the electrical connector engage. The lever arm is pivotally arranged on the PCB so that when the lever arm is arranged in a raised position the connector and socket are disengaged, whereas when the lever arm is lowered by application of force, the PCB is provided with a biasing force which serves to move the PCB in a direction guided by the guiding formations towards the socket thereby mating the first and second parts of the electrical connector. It will be appreciated therefore that there is a range of proximity of the PCB and the socket over which a resistive force is overcome in order to engage the two parts of the electrical connector, when the first and second parts of the connector come into contact. This provides a successful mating of the first and second parts to the effect of providing reliable electrical connection of the pins of the connector.
As will be appreciated however, the first and second parts of the electrical connector generally have a limited mating range. If the connector and socket are forced too closely together the first and/or second parts of the connector can be damaged. Damage can also occur to the components on the PCB or on the system chassis or circuit board back plane. Any damage can cause a failure in the electrical connection provided by the pins of the connector. Conversely, if the two parts are not mated closely enough the two parts of the connector will not fully engage which also thereby causes an unreliable electrical connection.
Accordingly, it will be appreciated that it is desirable to provide an ejector mechanism which provides reliable electrical connection between the two parts of the electrical connector.
Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims.
One aspect of the present invention provides an ejector mechanism for a circuit board and back plane operable to provide resiliently biased engagement between a first part of an electrical connector and a mutually engaging second part of the electrical connector. The first and second parts of the electrical connector provide electrical connection for a plurality of electrical channels between the circuit board on which the first part is mounted and the back plane on which the second part is mounted. The ejector mechanism comprises an engaging projection and a lever arm pivotally mounted on one of the circuit board and the back plane and configured to engage the engaging projection forming part of the other of the circuit board and the back plane. The lever arm is operable to apply an engaging force to the circuit board with respect to the back plane, when moved from a first position to a second position, which engaging force causes the first and second parts of the connector to engage. The engagement of the lever arm and the engaging projection is thus provided by a flexible coupling which allows relative movement of the circuit board away from the back plane and a biasing force which biases the circuit board towards the back plane.
During manufacture although the dimensions of the parts of the electrical connector, the circuit board and the back plane are known, variations in tolerances during manufacture can cause the first and second parts of the electrical connector to be either forced too far towards each other thus causing damage to the parts of the connector or indeed the circuit board and back plane itself, or not forced enough, the first and second parts being not pushed far enough together. As such, at the extremes of the range of the tolerance, the two parts of the connector may either not have a close enough fit or may be forced together as a result of being a too close fit thereby reducing in either case the reliability of the electrical connection. Furthermore, it is often a requirement for some electronic systems to withstand a degree of shock. For example, servers and telecommunications exchanges are often required to withstand a shock from, for example, an earthquake. As such the electrical connection formed between the first and second parts must remain competent in spite of a degree of shock.
An embodiment of the ejector mechanism according to the present invention addresses this technical problem by providing a flexible coupling between the lever arm and the engaging projection which allows relative movement of the circuit board away from the back plane and a biasing force which biases the lever arm or engaging projection towards the back plane. The flexible coupling provides an advantage in allowing the circuit board to move away from the back plane to the effect that if the tolerances between the circuit board and back plane are such that the force provided by the lever arm strains the first and second parts of the electrical connector as a result of the circuit board being a too close fit, the relative movement away from the back plane provided by the lever arm serves to relieve this strain. In contrast, if the tolerances combine to the effect that the two parts of the electrical connector are not sufficiently engaged, then the biasing force provided by the flexible coupling can improve the reliability of the electrical connection of the two parts.
The term back plane as used herein refers to and includes any member to which electrical connection of the circuit board is required. As such the back plane may itself be a circuit board, or may be a system chassis containing several such circuit boards.
In one embodiment the flexible coupling is provided by the engaging projection, which is formed from a resiliently deformable material, the material providing the relative movement and the biasing force of the circuit board towards the back plane. Thus by making the engaging projection resiliently deformable the circuit board may move away from the back plane whilst the engaging projection is biased towards the back plane as a result of the resilience of the material.
In an alternative embodiment the flexible coupling is provided by the engaging projection being formed by a rigid member and being slidably mounted on the back plane and a biasing member connected to the back plane and to the engaging projection, the slidably mounted engaging projection providing the relative movement and the biasing member providing the biasing force for biasing the circuit board towards the back plane. The biasing member may be a spring or a resiliently deformable member.